Optimization of systems, which generate electricity or other forms of energy, is normally at most a one-time design issue. In general, the power transfer of the system is calculated once, at the time of design, or even never, and then it is assumed that the system will be operated at designed specifications thereafter.
An example of such a system is a vehicular engine and alternator combination. The alternator device acts as a load and generates power in the form of electricity from the mechanical power provided by the engine. (One could trace the source of power back another step: the mechanical power that is available is dependent upon the rate at which hydrocarbons are combusted).
Energy is defined as the ability to do work and is a conserved quantity. Work can be defined as a force that acts through a distance. Work can be conceptualized as energy consumed. Power is the rate at which work is consumed.
From an engineering perspective, work performed, in most cases, refers to useful work. The rate at which useful work is performed is expressed mathematically as:power=work/time
Efficiency can be thought of as a measurement of how much of the available energy was actually consumed to do useful work. Another way to conceptualize efficiency is:efficiency=power available for useful work/power provided
In the combustion engine alternator electrical power generating system, mechanical power is converted into electrical power that is consumed by various electrical loads in the vehicle. However only a portion of the mechanical power that was provided is converted to electrical power, to be used in a specific manner. The power losses can mostly be accounted for as heat losses caused by friction in the conversion process from one form of power to another.
There are many factors that affect the efficiency with which power is converted from one form to another: such as from mechanical power to electrical power. For example: the typical automobile alternator is designed to run efficiently between 2 to 4 thousand revolutions per minute. An application, such as a racing engine, may have the alternator running outside of its intended range of 2 to 4 thousand RPM, causing unattractive power losses. It is desirable to increase the efficiency of such devices.
Typical fixed-installation power generation facilities such as solar plants, windmills and electrical generators of all types have similar problems. A great deal of ingenuity goes into designing the motive power source (for example, the blades of a windmill or the thermodynamic properties of an active “wet” solar panels system) so as to derive the maximum power from the source whether it is solar, mechanical or chemical or combinations of these sources including engines of all types. Usually these schemes involve viewing the source of power (the car engine, the windmill, etc) as the component to be optimized, while the electricity-generating device (or device converting one form of power to another form of power) is designed separately or later. When an average value for the power generation source is found, in terms of RPM or other valid metrics of power generation, then an electricity generating device of appropriate size and design RPM is attached as the load on the power source and allowed to run, regardless of power variations in the source, components wearing, or variations in other system parameters that ultimately affect the effectiveness of the power generation system.
The efficiency by which power is transferred from the power source to the load is influenced by loading and other power transfer considerations that affect the efficiency of system power output.
FIG. 1 is a simplified chart that illustrates generated power versus force (load, torque, counter torque) applied by the load in a typical power generating scenario where the input mechanical power is an engine with the “throttle” position set in a constant position that drives a generator/alternator. The force applied by the load is an electro-mechanical counter-torque used to generate electricity by the electrical generator/alternator (and may also consist of other power transfer parameters influencing generated power such as RPM, temperature, pressure etc). There is a fixed electrical load that is consuming the generated power.                Power=force*(distance/time)        As the counter torque (rotational force applied through a distance) is increased, RPM decreases.        An optimum power transfer occurs as a balance between applied force and RPM is reached at a force loading of 8, graph point 106.        
FIG. 1 shows that generated power does not necessarily increase as the electromechanical counter torque that the generator places on the driving engine is increased. FIG. 1 plots a graph demonstrating how the output generated electrical power varies as the electromechanical counter torque is increased on the driving engine. At zero levels of loading, such as a load between zero to one, illustrated in FIG. 1 in the area of point 102, no power from the driving engine is converted into its desired form, electrical power. A good analogy of this is an engine that is not hooked up to an alternator, or a turbine that is not hooked up to a generator or an alternator. No power can be generated without a load.
As the generator begins to convert more mechanical power into electrical power, it places a greater mechanical load on the driving engine. This relationship of increased generated power from the generator placing a greater mechanical load on the driving engine as it converts mechanical power into electrical power reaches a maximum at a load of between 7 and 9 in FIG. 1. (FIG. 1 is normalized and is unitless for generality). Between these points, maximum power transfer from the driving engine to the desired form, electrical power, has occurred. Unfortunately, as the electromechanical counter torque that the generator places on the driving engine continues to increase, the RPM begins to decline such that the product of torque*RPM results in less generated power. While FIG. 1 specifically illustrates generated electrical power versus force applied by load, it may also apply to mechanical power outputs, any type of input, and any type of load. An example would be a small windmill designed to pump water to livestock, having attached to it a quite large electricity-generating device such as a generator from a hydroelectric dam. Even if there is much wind, the windmill barely is able to turn over because of the large counter torque placed on it by the large generator and so little power is produced. If the wind slightly diminishes then the windmill is entirely overpowered by the load and ceases to turn, again resulting in no power generation, as might be depicted by point 110 on FIG. 1. Although there may be sufficient wind to allow generation of power by an alternative lighter load, no power is actually being generated by the large generator due to the mismatch of the load to its power source.
As mentioned previously, one solution is to match the components from the perspective of power transfer. An ideal system would include having a motor with a throttle position setting that produces a certain amount of horsepower at a specified optimal RPM matched with an electrical generator that generates the same amount of power as the motor at the optimal power producing RPM.
However, in the real world, an electrical generator system is confronted with many variables affecting the efficiency of power transfer from the driving engine to the final product, electrical power. Some of these variables will include power input fluctuations from engine throttling, system component wear resulting in changed performance characteristics, grade of fuel for an internal combustion engine and so on. Engineers may try to modify a system's drive device to try to cause it to perform efficiently within broad ranges. In many cases (such as a windmill) this is virtually impossible.
It is important to realize that when an engine is driving a load, such as an electromechanical load placed on it by an electrical generator, power related and efficiency characteristics of both the driving engine and the generator come into play as a system. For example at a specified throttle position, a combustion engine will convert fuel into rotational mechanical power most efficiently at a specified RPM. However a generator that this engine is intended to drive may convert rotational mechanical power to electrical power at an optimum RPM that is different than that of the driving engine. This is in fact the most likely case. In this simple system where the driving motor and the alternator are directly attached by a shaft, the throttle position is held constant, a constant electrical load is placed on the alternator, and the only variable is the electromechanical load placed on the motor by the generator that is optimized for maximum power transfer of the system as a whole; maximum power transfer will occur neither at the generator's optimum RPM nor at the engine's optimal RPM. Rather, maximum power transfer will occur at an RPM that will reflect all of the power transfer related characteristics of the whole system as it is influenced by the load, or other power transfer related characteristics. It would be preferable to provide a system in which power transfer parameter optimization is carried out for the device as a whole, and is carried out dynamically rather than statically.